This invention pertains to the manufacture by extrusion of profiled products made of expanded plastic materials; its object is to improve accommodation and shaping of the profiles downstream of the die.
A profile with a precise contour, composed of an expanded core and an external non-expanded layer, can be continuously manufactured by passing an expandable thermoplastic through a totally or partly annular die followed by rapid stiffening of the external layer of the parison by means of a cooled fixture of the same opening area as the external opening exit of the die, placed in the immediate vicinity of the die exit and coaxial therewith; expansion of the material occurs exclusively towards the interior of the profile and fills it more or less completely. This process is described in French Pat. Nos. 1,498,620 and 2,063,589.
In practice, the gap between the die and the cooling fixture, which varies between 0 and a few millimeters, usually between 5 and 20, is adjusted by the user according to the cross section of the profile to be produced and the various expandable thermoplastic formulations, to allow for a possible slight misalignment of the cooling fixture with respect to the die while still not allowing the parison to expand outwards as it emerges from the die, which would lead at best to a deterioration in the surface state of the profile and at worst to the risk of clogging of the parison before it enters the cooling fixture, leading to breakage of the profile.
It is difficult to obtain perfect alignment between the cooling fixture and the die since the latter forms a unit with the extrusion machine, while the cooling fixture is generally attached to a support placed opposite the machine and attached to the floor on rails. In addition, under the action of forces exerted by the drawing of the profile and friction between it and the cooling fixture, the initial alignment of the fixture with the die can be changed in the course of manufacturing and lead to breakages of the profile and therefore to production stoppages which are prejudicial to the productivity of the machine.